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Leather, Ink, and Miscellaneous: Gypsum

Gypsum. - Gypsum is a mineral which is found in nature in several forms. Chemically it consists of bihydrated calcium sulphate. It occurs in translucent crystals, as selenite; in massive forms and opaque crystals, as gypsum; in fine-grained partially translucent masses, as alabaster, and in a fibrous form, as satin spar.

When heated, gypsum gives off the water it contains and pulverizes into an opaque powder which, if moistened, quickly solidifies. This powder is known commercially as plaster of Paris . It is made by heating gypsum and grinding it to a fine powder.